A positive temperature coefficient thermistor is prepared from a sintered body of a ceramic material composition which has as a substrate BaTi0₃ with metallic oxide and has, in a predetermined voltage range, a voltage-current characteristic defined by the following equation:
wherein a is a constant value, Vx is a voltage on an axis of abscissa and Iy is a current on an axis of ordinate in a cartesian coordinate, said voltage range extending from a predetermined value to a value at least twice as much as the predetermined value so that when a voltage in said voltage range is applied to the sintered body, the sintered body provides heat at a substantially constant value. Thus, when the present invention is used in countries or areas in which commercial voltages of 110 V and 220 V are used, almost certain temperature can be obtained without changing voltage by a transformer.